Compliant gears have been used in various applications for shock absorbing purposes, for accommodating tolerance problems between meshing gear teeth and for reducing sound-generating vibrations caused by the meshing gear teeth.
In designing such a gear or gear systems, a yieldable material has been employed between a hub portion of the gear and a toothed ring portion of the gear. In essence, the yieldable material, such as rubber or other elastomer material, permits the gear teeth to move radially and torsionally relative to the rigid gear hub. Gear meshing problems are particularly prevalent in gear systems which employ parallel gear paths which require precise angular positioning of the gear teeth of a pair of gears on opposite sides of an output gear, for instance.
In designing compliant gears, it most often is desirable to have a fixed torsional stiffness for proper gear teeth meshing and power transmission. In other words, the gear teeth cannot twist beyond certain parameters based upon timing with other gears. On the other hand, the design must provide for radial stiffness to maintain center-line distances between the meshing gears as well as maintaining proper meshing geometry. The interrelationship between these parameters have constantly caused problems in gear design.
For instance, compliant gears conventionally have incorporated a single layer of elastomer material between a hub portion and a rim or ring gear portion of the gear. Elastomeric material, such as rubber, is an "incompressible fluid" and the torsional or radial stiffness thereof normally is a function of the thickness of the elastomer layer. Therefore, if a given torsional or sheer stiffness is desired, any change in the thickness of the elastomer layer for changing the radial stiffness would, of necessity, also change the torsional stiffness. Any change in the durometer of the elastomer layer also would change the torsional stiffness. Consequently, it is readily apparent that the simple use of an elastomer layer to provide a compliant gear has definite limitations This invention has solved many of these problems by providing a compliant laminate between the hub portion and the rim portion of the gear, the laminate including a rigid laminar shim sandwiched between a pair of elastomer layers. Such a novel construction provides considerably more radial stiffness but does not change the desired torsional stiffness in any given thickness of laminate between the hub and rim portions of the gear.
Much consideration also has been given in the past to reducing the sound-generating vibrations which accompany the meshing of gear teeth. Although the reduction of noise is desirable in any gear system which is intended to operate in the vicinity of human or animal hearing, the problem becomes particularly critical in designing apparatus, such as torpedos or other marine vessels, where noiseless and smooth operation is essential. Sound-generating vibrations are caused by the point where gears engage when the driving gear imposes a torque on the driven gear through contact between the mutually extending gear teeth. As successive gear teeth engage and disengage, it is apparent that a series of periodic compressive impulses are transmitted radially to the gear hub. These impulses are transmitted as vibrations from the hub to the gear shaft, from the shaft to the bearings, and to the supporting structure, where they emanate as sound from the larger gear casing surfaces. The sound is transmitted by waves through these components of the apparatus. Again, internal elastomer layers or structures have been employed for reducing the noise and undesirable vibrations caused by the meshing of the teeth in a pair of gears.
With the invention, by providing a laminate with an interior rigid laminar shim, the sound waves are broken to a considerably greater extent than prior compliant gears described above.